Koizumi called the finding a “grave violation of the import process,” with America.

USDA Secretary Mike Johanns said an investigation has begun to verify the claim. If confirmed, he called it a failure of the United States to comply with the recent agreement with Japan.

"While this is not a food safety issue, this is an unacceptable failure on our part to meet the requirements of our agreement with Japan,” Johanns said. “We take this matter seriously, recognizing the importance of our beef export market, and we are acting swiftly and firmly."

Meanwhile U.S. health officials have pledged additional aggressive steps to help ease concerns in Japan, where the population remains fearful of consuming beef infected with Bovine Spongiform Encephalopathy (BSE), or mad cow disease – a chronic, degenerative disorder affecting the central nervous system of cattle.

Officials in Washington, D.C, said they would take punitive action against the inspector who approved the shipment of meat that is in question, as well as close the plant that shipped the meat. Additionally, Johanns said he was immediately calling for USDA inspectors to make increased visits to processing plants across the nation.

"I have directed that additional USDA inspectors be sent to every plant that is approved to export beef to review procedures and ensure compliance with our export agreements, and I am requiring that two USDA inspectors review every shipment of U.S. beef for export to confirm that compliance,” he said. “I have also ordered unannounced inspections at every plant approved for beef export.”

Since Japan’s initial ban of U.S. beef beginning about two years ago, the domestic cattle industry has suffered financially. Exports to Japan from the United States once totaled nearly $1.7 billion annually, and domestic beef interests groups have been persistent to renew business.